A liquid chromatograph is composed of a plurality of units such as an auto sampler, a pump, and a column oven. The operation of each unit is controlled by means of the control signal from a control apparatus.
In recent years, a personal computer in which a control/process program has been installed is widely used as the control apparatus in such liquid chromatographs in order to generally control the analysis units and process the collected data. In such a control apparatus a schedule table is created before initiating an analysis so that multiple specimens can be continuously analyzed or other types of analysis can be automatically performed (for example, refer to JP-A 2005-127814).
FIG. 15 shows an example of a schedule table for a liquid chromatograph analysis. In this table, each row corresponds to an analysis. A row contains the information required to perform the analysis, such as the sample number, sample injection amount, method file name, data file name for storing the result of the analysis, and other information. A method file is a file in which the operation conditions (which will be hereinafter called an “analysis method”) of each of the units composing the liquid chromatograph are defined. A variety of parameters, such as the kind of mobile phase, the kind of column used in the analysis, the flow rate of the pump, the temperature of the column oven during the analysis, and other information, are also contained in the file.
After such a schedule table is created, and when an initiation of an analysis is commanded, samples are sequentially selected and the analysis conditions are set in accordance with the schedule so that the multiple samples are automatically analyzed.
In such a liquid chromatograph, a sample is analyzed under various conditions, in some cases, in order to find the best analysis conditions for the sample. This operation is called “method scouting.” In method scouting, the following operations are done: a user creates a number of different kinds of method files in advance in which the various parameters mentioned earlier are combined in various ways; the user specifies different method files in each row of a schedule table, as shown in FIG. 15; and the user instructs an initiation of the analysis with the same sample name and the sample injection amount for each row. Analyses are thereby performed sequentially under a variety of conditions in accordance with the description of the method file of each row. The chromatogram data resulting from the analyses are stored as one data file per analysis, and then saved in a memory unit such as a hard disk drive. The user refers to the chromatogram data stored in the memory unit to determine the analysis conditions under which the optimum analysis result was obtained in order to select the analysis method to be used for the sample.
One-known analysis method for a liquid chromatograph is a gradient solution sending method. In this method, solvents with different characteristics, such as water and organic solvents, are mixed, and a mobile phase liquid in which the mixture ratio of the solvents changes as time elapses is sent to a column. This method is particularly effective in adequately separating a sample composed of multiple components into the individual components.
In performing an analysis by using a gradient solution sending method (which will be hereinafter called a “gradient analysis”), a user sets a gradient profile such as that shown in FIG. 6 as an analysis parameter included in the method file. The gradient profile indicates the target values of the mobile phase composition over time from the initiation of an analysis. The example in FIG. 6 shows the profile of a gradient analysis in which the mixed liquid of solvent A and solvent B is used as the mobile phase and the mobile phase composition is expressed as the proportion of solvent B in the mixed liquid. A solvent that has a low elution capability (e.g. a highly polar solvent in the case of reverse mode) is used for solvent A. A solvent with a high elution capability (e.g. a low polar solvent in the case of reverse mode) is used for solvent B. At first, the amount of the solvent B is kept low until a predetermined period of time elapses from the injection of the sample at the point in time t0 (i.e. time t0 through t1). Consequently, the components contained in the sample are temporarily adsorbed in the column. The proportion of the solvent B increases in proportion to the time elapsed (time t1 through t2). As a result, the components are sequentially eluted from the column according to their characteristics (e.g. polarity). Subsequently, for a predetermined period of time (time t2 through t3), the proportion of solvent B is kept high so that the components remaining in the column are discharged from it. After that, the mobile phase composition returns to its initial state. This state is maintained for a predetermined period of time (time t3 through t4) so that the inside of the column is equilibrated.
Hereinafter, the process performed during the time t0 through t1 is called a sample introduction process. The process performed during the time t1 through t2 is called a gradient process. The process performed during the time t2 through t3 is called a washing process, and the one performed during the time t3 through t4 is called an equilibration process. In some cases, the sample introduction process may be omitted and the gradient process may be started simultaneously with the injection of a sample.